Strobe-type flashes using a gas-filled discharge tube are well known for use on still cameras for lighting a scene simultaneously with the taking of a still picture. Strobe-type flashes provide a significant amount of light for a fraction of a second that is sufficient to expose either film or imaging sensor contained in the associated still camera. Most point-and-shoot type cameras and some single lens reflex-type (SLR) still cameras have a strobe-type flash integrated with the camera. Further, most SLR cameras and some advanced digital models include a hot shoe to which an external flash module can be attached. The contacts on the hot shoe coordinate the activation of the flash with the shutter of the associated camera. Typical consumer grade point and shoot cameras both digital and film do not typically include a separate hot shoe.
Digital cameras have become very popular in the past few years. Digital cameras replace film with a permanent photosensitive sensor that captures a scene, which is then transferred in digital form to memory. An added benefit of digital cameras is that they are typically capable of recording video sequences in additional to still pictures. Early digital cameras were only capable of recording very low resolution video clips at low frame rates resulting in a video that was jerky and had only enough resolution to be properly viewed in a small window on a user's computer. With the advent of higher resolution sensors and faster electronics, many newer digital cameras are capable of recording video at frame rates and resolutions that make the videos suitable for playback on larger screens and even on televisions. The more advanced digital cameras even support frame rates and video resolutions rivaling analog and some digital video recorders.
The video capability is generally viewed as an add-on feature of digital still cameras rather than a primary feature. Digital still cameras are not optimized in design or features to fully realize the potential of their video recording capabilities. For instance, no continuous illumination source is provided to light a scene of which a video is being taken. Obviously, strobe-type flashes are useless for taking video given their extremely short duration. To cope with recording video in low light situations, the controller within a typical digital camera increases the gain of the sensor; however, as the gain increases, the sensor's level of electronic noise increases substantially thereby degrading the quality of the resulting video. Accordingly, the video capabilities of a typical digital still camera are not useful particularly useful in low light situations.
Within the last decade or so, extremely bright light emitting diodes (LEDs) have been developed. LEDs, which are extremely energy efficient, require only a fraction of the energy input as other sources of illumination, such as incandescent and fluorescent lights. Accordingly, for a similar amount of light output, battery-powered LED based illuminators can be made much smaller and much lighter than battery-powered illuminators using other light sources. For example, a LED-based flashlight running on button cell batteries can provide as much, if not more, light than a traditional incandescent-based flashlight using D, C or A sized batteries, and even have a runtime in excess of the incandescent-based flashlight.
Several prior art documents discuss the use of LED-based flashes in place of strobe-type units. One of the first mentions was in U.S. Pat. No. 4,866,285, wherein LEDs optimized to emit infrared light are incorporated into a hot shoe flash. This flash unit is taught to be utilized when a user is shooting infrared type film. In a traditional manner, the infrared LEDs flash in synchronization with the operation of the associated camera's shutter.
U.S. Patent Application #'s 2003/0160889 ('889) and 2003/0180037 ('037) both suggest the use of using one or more bright white light LEDs in place of a gas-filled discharge tube. In both, the LED's are contemplated for use in a traditional manner to provide a short duration pulse of light to illuminate a scene to facilitate the taking of a still picture, although the '889 reference does suggest providing a version of the camera incorporating a manually-activated switch to turn the LEDs on and off when the flash circuit is not coupled with the shutter trigger button. Both also contemplate having the flash incorporated into the camera, although the '037 reference also contemplates the flash being separately housed, but still electronically coupled to the camera to facilitate flash synchronization. Neither suggests the use of the continuous illumination of the LEDs for purposes of taking video using a digital still camera.